A rotor for a dynamoelectric machine typically comprises a cylindrical forging of magnetic metal having a plurality of longitudinal slots opening through the outer surface of the rotor at circumferentially spaced positions thereabout. Conductor bars are disposed in the slots for carrying current. The ends of the conductor bars are suitably connected with conductive end turns to form the required current pattern. Because the conductor bars and end turns give rise to resistive heating, certain dynamoelectric machines require additional cooling of the rotor endwindings. This is typically provided by grooved ventilation passages within the end turns and conductor slot bars through which cooling gas may flow.
The various ventilation schemes which make use of cooling grooves in the endwindings, however, introduce manufacturing complexities. One such complexity is that it is difficult to form or fabricate a well shaped, mechanically sound coil corner with a cooling groove passing through it. It is also somewhat difficult to maintain the shape of the cooling groove to proper tolerances when forming it around the coil corner. In addition, many of the present grooved endwinding ventilation schemes require complex baffling in the endwinding region to set up high and low pressure regions to properly channel the cooling gas into and out of the cooling grooves. Some of the baffling schemes require additional shaft machining to create mechanical support for the baffles.
Several approaches have been used to duct cooling gas from grooves in the circumferentially oriented end turns to grooves in the conductor slot bars. The simplest approach was to use round corner turns and let the duct follow the curvature of the corner. This approach, however, does not apply to designs with square corner windings.
For designs with square corner coils, twin layer turns are used to form ducts by laying together two grooved pieces of copper with the grooves facing each other. At the coil corner, a gusset is brazed in place as a means of joining the circumferential end turns to the conductor bars. At the coil corner, the gusset is also grooved so as to allow cooling gas to flow from the end turn to the conductor bar.
A third approach involves feeding the gas into each turn on both sides of the coil corner and ducting it away from the coil corner. This requires additional baffling in the pole center to create a low pressure region into which the gas in the end turns can flow which creates an undesirable amount of complexity.
A fourth approach, as described in Kaminski et. al., U.S. Pat. No. 4,543,503, makes use of single layer conductor bars and twin layer end turns. Gas is channeled away from the coil corners much like in the third approach described above.
A fifth approach, described in U.S. Pat. No. 4,814,655, requires the gas to flow through the reverse side of a single layer gusset. This involves an undesirable degree of pressure loss.
A sixth approach does not rely on internal ducts at all but rather channels all the gas externally via sinuous passages in the coil-to-coil blocking. This has the disadvantage of giving up the benefits of free convection cooling. It also creates a rigid endwinding structure which is not conducive to thermal expansion of the rotor winding.